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Appendix II.

795

There is a rapid decrease in strength with any further increase
in manganese. It should be .noted that the carbon must be kept
down to i% in the 14% material, to do which the ferro-manganese
should have about 82% of Mn. No doubt if the carbon could be
sufficiently decreased, even 20 or 25% Mn could be added. The
ingots are from 28 to 30 cwts., and the ferro-manganese is
added in a molten state. Honeycombing is not bad, but the
centre of the ingot' pipes' considerably on account of the great
contraction of this steel.

FORGED MANGANESE STEEL

Percentage                      (Water quenched).

of Mn.
10     : Ductility equal to mild steel, strength much greater.

13      : Still higher strength and ductility.

14      : Limit of manufacture: beyond this toughness decreases.

Finally, manganese steel is strong, ductile, and hard; free from
blowholes, and more fluid than cast steel, but pipes badly, and
requires good feeding gates to mould. Its hardness prevents
machining or fitting, and grinding only can be adopted. The
steel is suited to dredger pins and other articles subject to great
wear ; and is also useful for wheel tyres in conjunction with chilled
brake blocks, causing great grip. The following is an analysis :

Carbon.

Silicon.

Manganese.

and the strength and ductility are next shewn:

Percentage Mn.

2\ to 7| 
2\ to 7j 

'4       "

Breaking Stress sq. in.
Cast         3^ tons
Forged     25 tons

very brittle
3% elongation

38 to 50% elongation

(as against Basic cast steel: 22 to 27 tons: 26 to 30% elongation).

In the testing machine the material is semi-plastic from the
commencement, shewing permanent set with low loads.

Nickel Steel is a very valuable material, discovered about
1885, in the search for combined strength and ductility, which
carbon alone is unable to give to iron. But when it is said that